1. Field of the Invention
The present invention relates to a semiconductor circuit, a battery monitoring system, and a control method. The present invention specifically relates to a semiconductor circuit for monitoring battery voltages, a battery monitoring system, and a control method.
2. Description of the Related Art
Generally, batteries (specific examples include lithium-ion batteries) in which plural batteries (battery cells) are connected in series are used as large-capacity, high-output batteries used for driving motors in hybrid vehicles and electric vehicles.
In this kind of battery, there are cases where a difference occurs in the battery voltages between the batteries due to variations in the characteristics of the batteries, for example, such as in a case where the battery is repeatedly charged and discharged. Overcharge and overdischarge occur when the battery is used in a state in which a difference has occurred in the battery voltages, and there are cases where problems such as the life of the battery overall becoming shorter occur. For this reason, the battery voltages in the batteries are monitored with a battery monitoring system, and the battery voltages of the batteries are equalized by discharging any battery whose battery voltage is greater than the others.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2009-213196 discloses a capacity regulating device (a battery monitoring system) that is equipped with a capacity adjusting circuit formed by capacity adjusting resistors connected in parallel to batteries and switching circuit elements connected in series to the capacity adjusting resistors. Thermistor elements are disposed between drive terminals of the switching circuit elements and one terminal each of the switching circuit elements connected to negative electrodes of the batteries. This technology discharges the batteries by switching on the switching circuit elements.
However, in the aforementioned technology, there are cases where variations occur in the battery voltages despite the discharge for equalizing the battery voltages of the batteries.
FIG. 13 illustrates a related art battery monitoring system 100. The related art battery monitoring system 100 is configured to include a battery cell group 112, a discharge circuit 113, and an equalization switching element drive circuit 121 that supplies charge to control terminals of equalization switching elements SW of the discharge circuit 113.
In the discharge circuit 113, the equalization switching elements SW and resistive elements Rbal, which are for limiting the discharge quantity and are connected in series between high potential sides and low potential sides of battery cells C, and resistive elements Rcb, which are pull-down resistors, are disposed for each battery.
In the battery monitoring system 100, in the case of performing discharge of the battery cells C, charge is supplied from the equalization switching element drive circuit 121 to gates of the equalization switching elements SW disposed for those battery cells C to thereby switch on the gates, whereby those battery cells C are short-circuited and discharged.
FIG. 13 illustrates a state in which the battery cell Cn is discharged. In the case of discharging the battery cell Cn, charge is supplied from the equalization switching element drive circuit 121 via a terminal CBn to the gate of the equalization switch element SWn (see the bold, solid arrow in FIG. 13). When the equalization switching element SWn is switched on, the high potential side and the low potential side of the battery cell Cn are short-circuited so that the battery cell Cn is discharged.
At this time, the charge supplied from the equalization switching element drive circuit 121 ends up being supplied via the resistive element Rcbn to the high potential side of the battery cell Cn−1 placed on the low potential side (see the bold, dashed arrow in FIG. 13). For this reason, the battery cell Cn−1 ends up being charged by the charge.
When the battery cell Cn−1 ends up being charged in this way, there are cases where the problem that the battery voltages of the battery cells end up varying occurs.